Season of Retreating Monsoon

The retreating monsoon is not a season of dramatic winds or heavy rain across the whole country. It is a season of transition — the southwest monsoon withdrawing, the sun moving south, and the weather turning hot and humid before the cooler winter sets in. The months of October and November carry this name, and their character changes sharply depending on where you are in India.

Why the monsoon retreats

The whole mechanism rests on the low-pressure trough over the Ganga plain. Through the summer, this trough pulls in the moisture-laden southwest winds. By the end of September, the sun begins its southward march, and the trough responds by shifting southward too. As it moves, the southwest monsoon loses its strength. The retreat is gradual and follows a clear timetable:

• By the first week of September, the monsoon withdraws from western Rajasthan.
• By the end of September, it has pulled out of Rajasthan, Gujarat, the western Ganga plain, and the Central Highlands.
• By the beginning of October, the low-pressure centre covers the northern parts of the Bay of Bengal.
• By early November, it moves over Karnataka and Tamil Nadu.
• By the middle of December, the centre of low pressure is completely gone from the Peninsula.

So the retreat takes roughly three months, moving from the northwest of the country down to the southeast.

October heat

Once the rain-bearing winds leave, the skies clear up. With the sun still strong and the land still moist from the monsoon, the combination of high temperature and high humidity makes the air feel heavy and suffocating. This oppressive weather is known as the October heat. It is a distinctive feature of the retreating season, felt most in the northern plains.

The relief comes in the second half of October, when the mercury begins to fall rapidly, especially in northern India. The clear skies and the southward-moving sun finally bring down the temperatures, easing the discomfort.

Two very different weathers

The retreating monsoon season splits India into two contrasting halves:

• North India — the weather is dry. The monsoon has left, the skies are clear, and there is little rain.
• Eastern Peninsula — this is the rainiest time of the year. October and November are the wettest months for this region, especially along the Coromandel coast.

The rain in the Peninsula is not from the monsoon winds themselves. It comes from cyclonic depressions that originate over the Andaman Sea. These depressions travel westward and cross the eastern coast of the southern Peninsula, bringing widespread rain.

Tropical cyclones and their destruction …